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Gene Testing Advantages and Limitations - Genetic Test Applications
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Gene tests which are also called DNA-based tests are the most recently used techniques for detecting any genetic disorder .such tests directly involve direct examination of the DNA molecule itself. This process involves extraction of DNA from blood sample or from other body fluids or tissues. The DNA change can vary from small piece or even an entire chromosome which is visible under a microscope. Some genes may be over expressed or inactivated and with some kind of mutation.
Genetic testing in a broader sense includes biochemical tests for the presence or absence of key proteins that signal aberrant genes.

Genetic tests are used for several reasons, including:
• Carrier screening, which involves identifying unaffected individuals who carry one copy of a gene for a disease that requires two copies for the disease to be expressed.
• preimplantation genetic diagnosis
• prenatal diagnostic testing
• newborn screening
• presymptomatic testing for predicting adult-inception disorders such as Huntington's disease
• Presymptomatic testing for estimating the risk of developing adult-beginning cancers and Alzheimer's disease.
• Conformational diagnosis of a symptomatic individual.
• forensic/identity testing

For some types of genetic tests, small pieces of DNA are designed which are termed as probes whose sequences are complementary to the mutated sequences. These probes will seek their complement among the three billion base pairs of an individual's genome. If the mutated sequence is present in the patient's genome, the probe will bind to it and flag the mutation. Another type of DNA testing involves comparing the sequence of DNA bases in a patient's gene to a normal version of the gene. Cost of testing can range from hundreds to thousands of dollars, depending on the sizes of the genes and the numbers of mutations tested.

BENEFITS OF GENE TESTING
A negative result obtained can relieve lot of tension and can eliminate the need for frequent checkups. In case of person who has the family history of cancer can be relieved of unwanted fear. In case the person is diagnosed positive for a particular disease he can be informed and healthy decisions can be made about the future treatments. It can also let a person take steps to reduce risk before disease has a chance to develop

Gene testing can allow families to avoid having children with devastating diseases or identify people at high risk for conditions that may be preventable.

LIMITATIONS OF GENE TESTING
• For example, some disorders that "run in families" can be traced to shared environmental exposures rather than any inherited susceptibility. In addition, some mutations detected by a positive test may never lead to disease. Furthermore, because existing tests look only for the more common mutations in a gene, some disease-causing mutations may escape detection.
• A limitation of all medical testing is the possibility for laboratory errors. These might be due to sample misidentification, contamination of the chemicals used for testing, or other factors.
Many in the medical firm feel that uncertainties surrounding test interpretation, the current lack of available medical options for these diseases, the tests' potential for provoking anxiety, and risks for discrimination and social stigmatization could overshadow the benefits of testing.

SOME CURRENTLY AVAILABLE DNA-BASED GENE TESTS

• Alpha-1-antitrypsin deficiency (AAT; emphysema and liver disease)
• Amyotrophic lateral sclerosis (ALS; Lou Gehrig's Disease; progressive motor function loss leading to paralysis and death)
• Alzheimer's disease* (APOE; late-onset variety of senile dementia)
• Ataxia telangiectasia (AT; progressive brain disorder resulting in loss of muscle control and cancers)
• Gaucher disease (GD; enlarged liver and spleen, bone degeneration)
• Inherited breast and ovarian cancer* (BRCA 1 and 2; early-onset tumors of breasts and ovaries)
• Hereditary nonpolyposis colon cancer* (CA; early-onset tumors of colon and sometimes other organs)
• Central Core Disease (CCD; mild to severe muscle weakness)
• Charcot-Marie-Tooth (CMT; loss of feeling in ends of limbs)
• Congenital adrenal hyperplasia (CAH; hormone deficiency; ambiguous genitalia and male pseudohermaphroditism)
• Cystic fibrosis (CF; disease of lung and pancreas resulting in thick mucous accumulations and chronic infections)
• Duchenne muscular dystrophy/Becker muscular dystrophy (DMD; severe to mild muscle wasting, deterioration, weakness)
• Dystonia (DYT; muscle rigidity, repetitive twisting movements)
• Emanuel Syndrome (severe mental retardation, abnormal development of the head, heart and kidney problems)
• Fanconi anemia, group C (FA; anemia, leukemia, skeletal deformities)
• Factor V-Leiden (FVL; blood-clotting disorder)
• Fragile X syndrome (FRAX; leading cause of inherited mental retardation)
• Galactosemia (GALT; metabolic disorder affects ability to metabolize galactose)
• Hemophilia A and B (HEMA and HEMB; bleeding disorders)
• Hereditary Hemochromatosis (HFE; excess iron storage disorder)
• Huntington's disease (HD; usually midlife onset; progressive, lethal, degenerative neurological disease)
• Marfan Syndrome (FBN1; connective tissue disorder; tissues of ligaments, blood vessel walls, cartilage, heart valves and other structures abnormally weak)
• Mucopolysaccharidosis (MPS; deficiency of enzymes needed to break down long chain sugars called glycosaminoglycans; corneal clouding, joint stiffness, heart disease, mental retardation)
• Myotonic dystrophy (MD; progressive muscle weakness; most common form of adult muscular dystrophy)
• Neurofibromatosis type 1 (NF1; multiple benign nervous system tumors that can be disfiguring; cancers)
• Phenylketonuria (PKU; progressive mental retardation due to missing enzyme; correctable by diet)
• Polycystic Kidney Disease (PKD1, PKD2; cysts in the kidneys and other organs)
• Adult Polycystic Kidney Disease (APKD; kidney failure and liver disease)
• Prader Willi/Angelman syndromes (PW/A; decreased motor skills, cognitive impairment, early death)
• Sickle cell disease (SS; blood cell disorder; chronic pain and infections)
• Spinocerebellar ataxia, type 1 (SCA1; involuntary muscle movements, reflex disorders, explosive speech)
• Spinal muscular atrophy (SMA; severe, usually lethal progressive muscle-wasting disorder in children)
• Tay-Sachs Disease (TS; fatal neurological disease of early childhood; seizures, paralysis)
• Thalassemias (THAL; anemias - reduced red blood cell levels)
Timothy Syndrome (CACNA1C; characterized by severe cardiac arrhythmia, webbing of the fingers and toes called syndactyly, autism)




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Gene Testing Advantages and Limitations - Genetic Test Applications00